The invention relates to reducing message traffic in an intelligent network, particularly between a service switching point and a service control point.
An intelligent network (IN) is able to provide a subscriber of a telecommunications network, such as a wired network or a mobile telephone network, with a plurality of various services. Such services include a virtual private network (VPN) which allows the use of short numbers between subscribers belonging to a local network, and a personal number in which the intelligent network reroutes the calls directed to a personal number in a manner controlled by the subscriber. An example of such an intelligent network is described in recommendations of the ITU-T Q-1200 series, of which Q-1210 to Q-1219 define a set of features known as CS-1 (Capability Set 1), and correspondingly, Q-1220 to Q-1229 define a set of features CS-2. The invention and its background will be described by the terminology of recommendation ETS 300 374-1 CorelNAP, but the invention can also be employed in intelligent networks implemented according to other intelligent network standards.
A basic call state model (BCSM), defined in connection with the intelligent network, describes different stages of call control and defines the points in which call control can be interrupted in order to start an intelligent network service. It identifies the detection points in the call and connection process in which service logic entities of the intelligent network can have an interactive relationship with basic call and connection management features.
In conventional call set-up which takes place without the help of an intelligent network, telephone exchanges make independently all the deductions about call routing. One or more service control functions (SCF) are associated with intelligent network architecture. The equipment or network element carrying out the tasks determined for the SCF is called a service control point (SCP). In the present invention, SCF and SCP are equal, and will hereinafter be called SCP. The SCP gives call set-up instructions to the exchange, or the exchange may inquire call set-up instructions from the SCP. If the interface of subscriber B is found to be busy at some stage of call set-up, for example, the call can be directed to an alternative number. FIG. 1 also shows other elements of an intelligent network which are relevant to the understanding of the invention, such as a call control function (CCF) comprising high-level call handling functions of the exchange, such as establishing and releasing transfer connections. Service data function SDF and service data point SDP form a database comprising subscriber-specific and/or service-specific information. Specialized resource function SRF is an interface for network mechanisms associated with interaction with a subscriber. It can be associated with what are known as intelligent peripherals (IP) and comprise e.g. more advanced speech handling functions than do exchanges in general.
Service switching function (SSF) is an interface between the call control function CCF and the service control function SCF. The network element performing the SSF is called a service switching point (SSP). An intelligent network service is produced by the service switching point SSP inquiring instructions from the service control point SCP by means of messages to be transmitted across the SSP/SCP interface upon the encounter of detection points associated with the services. In intelligent network terminology these messages are called operations. In association with an intelligent network service, a service program is started at the service control point SCP, the operation of the program determining the operations transmitted by the SCP to the SSP at each stage of a call.
FIG. 2 shows the operation of a prior art intelligent network at detection points. In step 2-1 the SSP transmits to the SCP an InitialDP operation containing the necessary data for setting up a call. Next the detection points are armed in the SSP. In step 2-2 the SCP transmits to the SSP a message RequestReportBCSMEvent, informing the SSP which encounters of the detection points it is to report to the SCP. Next, in step 2-3, the SCP typically transmits charging and/or interaction operations, such as FurnishChargingInformation (record charging information associated with the intelligent network service) or PlayAnnouncement (supply subscriber with an announcement associated with the intelligent network). In step 2-4 the SCP transmits to the SSP a routing instruction, such as CollectInformation (collecting dialing information from the subscriber), Connect (route call to a new number), Continue (continue call set-up with the same data) or ReleaseCall (release the connection). In intelligent network recommendations, call set-up is divided into given rough phases called Point-In-Call (PIC). It is possible that the SSP has been configured to continue call set-up from phase PIC 2 in response to a CollectInformation operation and to continue call set-up from PIC 3 in response to a Connect operation, etc.
There are two kinds of detection points. The above events in FIG. 2 relate to a detection point called a Trigger Detection Point (TDP). The SSP may make an initial inquiry to the SCP in connection with such a TDP detection point, and receives instructions for call set-up. Another type of detection point is what is known as an event detection point (EDP). 2-5 in FIG. 2 shows the instant when such an EDP detection point is encountered during call set-up. The SSP reports the encounter of the detection point to the SCP which transmits more call set-up instructions to the SSP in step 2-7.
The problem in this arrangement is first of all a significant message traffic across the SSP/SCP interface. This message traffic and the large number of service programs comprised by the service control point SCP also slow down the operation of the service programs because of loading delays.